The present invention relates to compositions used as adhesives, and in particular to two-part epoxide adhesive compositions having improved peel and shear strength.
Epoxy-based adhesives are utilized for providing high quality, permanent bonding in many different commercial and industrial settings. Epoxy-based adhesives are especially useful for their ability to strongly adhere to a variety of materials, including metal, glass, plastic, wood and fiber. Consequently, these adhesives are often used to bond dissimilar materials together. Epoxy-based adhesives also provide the benefit of excellent resistance to attack by many corrosive chemicals. Because of these properties, these adhesives are often utilized in place of metal solder which, in contrast to epoxy, may contain toxic metals and require fluxing.
Two forms of epoxy-based adhesive compositions are commonly commercially available. The first form, one-component adhesives, are available as rigid epoxy adhesives, frozen pre-mix flexible epoxy adhesives, and room-temperature stable flexible epoxy adhesives. While one-component compositions provide the convenience of storage as a single component, they also require elevated curing temperatures. The second form of adhesive, two-component adhesives, are stored as two separate components that are mixed prior to application on the surfaces to be bonded together. Two-component adhesives overcome the often inconvenient curing requirements of one-component adhesives in that two-component adhesives are curable at room temperature.
Two critical measurements of adhesives are peel strength and shear strength. Generally, epoxy adhesives are brittle materials that fail when subjected to peel forces. Thus, epoxy adhesives are unsuitable for applications that require the adhesives to be subjected to damaging external forces. Consequently, there is a need in the art for the development of an epoxy adhesive having improved peel and shear strength which would provide resilient bonds when subjected to external forces. Such adhesives would advantageously include additives to provide the adhesive with the ability to withstand peel forces and increase the shear strength of the adhesive, but would not require the adhesive to be cured at high temperatures.
The present invention discloses a two-component epoxy-based adhesive comprising a resin component and a curing agent component. The resin component comprises an epoxy resin, a toughener that is preferably a polymer polyol and, optionally, fumed silica. The curing agent comprises a polyoxyalkyleneamine, an amine terminated butadiene-acrylonitrile polymer, tertiary amine, polyamide resin, silane and fumed silica. The adhesive composition is particularly useful for bonding of metals, plastics and composites and for functions such as laminating, honeycomb bonding, automotive assembly and construction assembly.
Another embodiment of the invention is directed to a method for bonding materials together which comprises applying the adhesive composition of the invention in a liquid or paste form to a first substrate, bringing a second substrate in contact with the composition applied to the first substrate, and subjecting the applied composition to conditions which will allow the composition to cure to an irreversible solid form. Still another aspect of the invention is directed to an article of manufacture comprising the adhesive of the invention.
The two-component epoxy-based adhesive of the present invention comprises resin and curing agent components. The resin component comprises an epoxy component, one or more polymer polyols and, optionally, fumed silica.
Examples of epoxy resins suitable for use in the present adhesive composition include monofunctional and multifunctional glycidyl ethers of Bisphenol-A and Bisphenol-F, and cycloaliphatic epoxy resins or a combination thereof. The cycloaliphatic epoxides are preferably selected from non-glycidyl ether epoxides containing more than one 1.2 epoxy group per molecule. These epoxides are characterized by a ring structure wherein the epoxide group may be part of the ring or may be attached to the ring structure. Examples of non-glycidyl ether epoxides include 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate, which contains two epoxide groups that are part of the ring structures and an ester linkage, vinylcyclohexene dioxide, which contains two epoxide groups and one of which is part of the ring structure, 3,4-epoxy-6-methyl cyclohexyl methyl-3,4-epoxycyclohexane carboxylate and dicyclopentadiene dioxide.
Glycidyl ether epoxides are preferred in the invention, either separately or in combination with the non-glycidyl ether epoxides. These resins are selected from glycidyl ether epoxides containing more than one 1.2 epoxy group per molecule. A preferred epoxy resin of this type is Bisphenol A resin. Preferred Bisphenol A type resin includes 2,2-bis(4-hydroxyphenyl) propane-epichlorohydrin copolymer. A further preferred epoxy resin is Bisphenol F type resin. These resins are generally prepared by the reaction of one mole of bisphenol F resin and two moles of epichlorohydrin. A further preferred type of epoxy resin is epoxy novolac resin. Epoxy novolac resin is commonly prepared by the reaction of phenolic resin and epichlorohydrin. A preferred epoxy novolac resin is poly(phenyl glycidyl ether)-co-formaldehyde. Biphenyl type epoxy resin may also be utilized in the present invention. This type of resin is commonly prepared by the reaction of biphenyl resin and epichlorohydrin. Dicyclopentadiene-phenol epoxy resin, naphthalene resins, epoxy functional butadiene acrylonitrile copolymers, epoxy functional polydimethyl siloxane and mixtures thereof are additional types of epoxy resins which may be employed. The preferred epoxy for the adhesive of the present invention is a blend of Bisphenol F type resin and Bisphenol A type resin, commercially available from Vantico as ARALDITE PY720. Other suitable Bisphenol A/F blends commercially available include EPIKOTE 235, 234 and 238 (Shell), NPEF 185, 198 and 187 (Whyte Chemicals), DER 351, 356 and 352 (Dow), or RUTAPOX 0169 or 0166 (Bakelite). Bisphenol F type resin is available from CVC Specialty Chemicals under the designation 8230E, EPIKOTE 862 (Resolution), or Whyte Chemicals as NPEF 170. Bisphenol-A type resin is commercially available from Resolution Technology as EPON 828, 828EL or 828XA. The epoxy resin component of the resin comprises from about 50 to about 90 weight percent of the resin component and, preferably, about 75 to about 85 weight percent of the resin component.
The toughener segment of the resin component is preferably a polyol and most preferably a polyester or polyether polyol. Examples of polyether polyols include a linear and/or branched polyether having plural numbers of ether bondings and at least two hydroxyl groups, and contain substantially no functional group other than the hydroxyl groups. Examples of the polyether polyol may include polyoxyalkylene polyol such as polyethylene glycol, polypropylene glycol, polybutylene glycol and the like. Further, a homopolymer and a copolymer of the polyoxyalkylene polyols may also be employed. Particularly preferable copolymers of the polyoxyalkylene polyols may include an adduct at least one compound selected from the group consisting of ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, 2-ethylhexanediol-1,3,glycerin, 1,2,6-hexane triol, trimethylol propane, trimethylol ethane, tris(hydroxyphenyl)propane, triethanolamine, triisopropanolamine, ethylenediamine and ethanolamine; with at least one compound selected from the group consisting of ethylene oxide, propylene oxide and butylene oxide.
A number of suitable polyols are commercially available. Non-limiting examples include CP4701 (Dow Chemicals), NIAX 11-34 (Union Carbide Corp), Desmophen 3900 (Bayer), Propylan M12 (Lankro Chemicals), Highflex 303 (Daiichi Kogyo Seiyaku K.K.) and Daltocel T 32-75 (ICI). xe2x80x9cPolymer polyolsxe2x80x9d are also suitable, e.g., graft polyols containing a proportion of rubber copolymers, polymerized in situ, e.g., NIAX 34-28 (Union Carbide Corp.), Caradol MD32-04 (Shell), Desmophen 1920D and Arcol 1366 (Bayer).
Polyester polyols are formed from the condensation of one or more polyhydric alcohols having from 2 to 15 carbon atoms with one or more polycarboxylic acids having from 2 to 14 carbon atoms. Examples of suitable polyhydric alcohols include ethylene glycol, propylene glycol such as 1,2-propylene glycol and 1,3-propylene glycol, glycerol, pentaerythritol, trimethylolpropane, 1,4,6-octanetriol, butanediol, pentanediol, hexanediol, dodecanediol, octanediol, chloropentanediol, glycerol monallyl ether, glycerol monoethyl ether, diethylene glycol, 2-ethylhexanediol-1,4, cyclohexanediol-1,4, 1,2,6-hexanetriol, 1,3,5-hexanetriol, 1,3-bis-(2-hydroxyethoxy)propane and the like. Examples of polycarboxylic acids include phthalic acid, isophthalic acid, terephthalic acid, tetrachlorophthalic acid, maleic acid, dodecylmaleic acid, octadecenylmaleic acid, fumaric acid, aconitic acid, trimellitic acid, tricarballylic acid, 3,3xe2x80x2-thiodipropionic acid, succinic acid, adipic acid, malonic acid, glutaric acid, pimelic acid, sebacic acid, cyclohexane-1,2-dicarboxylic acid, 1,4-cyclohexadiene-1,2-dicarboxylic acid, 3-methyl-3,5-cyclohexadiene-1,2-dicarboxylic acid and the corresponding acid anhydrides, acid chlorides and acid esters such as phthalic anhydride, phthaloyl chloride and the dimethyl ester of phthalic acid. Preferred polycarboxylic acids are the aliphatic and cycloaliphatic dicarboxylic acids containing no more than 14 carbon atoms and the aromatic dicarboxylic acids containing no more than 14 atoms.
Commercially available polyols which may be used in the practice of the invention include polyethers such as ARCOL PPG 2025 (Bayer), PolyG 20-56 (Arch) and Pluracol P-2010 (BASF), polyesters such as Dynacoll 7360 (Creanova), Fomrez 66-32 (Crompton) and Rucoflex S-105-30 (Bayer) and polybutadiene such as Poly BD R-45HTLO (Elf Atochem). A most preferred polyol is polyoxypropylene/polyoxyethylene non-reactive styrene acrylonitrile polymer polyol (ARCOL HS100; Bayer). Additional preferred polyols are STEPANPOL, commercially available from Stepan Company, polybutadiene resin (Poly BD 600 and 605), and polytetramethylene ether glycol molecular weight 1000 and 2000 (TERATHANE 1000 and 2000). Other materials that may be utilized as tougheners include acrylate monomers, such as epoxidized soya bean acrylate (CN111; Cray Valley) and dipropylene glycol diacrylate (SR508; Cray Valley). The toughener segment of the resin component comprises from about 10 to about 40 weight percent of the resin component and, preferably, about 10 to about 20 weight percent of the resin component.
The final ingredient in the resin component is silica which provides non-slump properties to the material. While the adhesive may be formulated without silica, its absence will result in a material that will have a very low viscosity and thus could flow out of the joints during application and curing, thus leaving very little of the adhesive to bond the surfaces. Preferably the silica is hydrophobic fumed silica, such as is commercially available from Cabot as CABOSIL TS-720 or from Degussa as AEROSIL R202. The silica segment of the resin component comprises from about 0 to about 10 weight percent of the resin and, preferably, about 0 to about 5 weight percent of the resin component.
The curing agent component of the adhesive composition includes an amine component. Among the various types of amine that may be useful are one or more of polyether urethane amine, amino polyamide, polyether polyamine, dimethylaminopropylamine, and polyaminoimidazoline resin. Among the commercially available forms of these amines are EUREDUR 70, EUREDUR 75, EUREDUR 140, EUREDUR 145, EUREDUR 76 (available from Vantico under the ARADUR tradename) and CRAYAMID 125 (Cray Valley). A most preferred form of amine is polyoxyalkyleneamine of molecular weight 230, commercially available as JEFFAMINE D230 (Huntsman). The amine component of the curing agent comprises about 20 to about 100 wt % of the curing agent, and is preferably about 40 to about 80 wt % of the curing agent.
A further component of the curing agent is an amine terminated butadiene-acrylonitrile (ATBN) polymer, such as HYCAR ATBN 1300xc3x9716 (Noveon). The ATBN component of the curing agent comprises about 0 to about 30 wt % of the curing agent, and is preferably 10 to about 20 wt % of the curing agent.
A phenolic accelerator component is also included in the curing agent. A most preferred phenol is tris(2,4,6-dimnethylaminomethyl)phenol (Curing Agent K54 (Air Products)), Permacure 213 (Whyte Chemicals), or ARADUR 13 (Vantico). Additional components of the curing agent include a polyamide resin based on dimerised fatty acid and polyamine (CRAYAMID 125 (Cray Valley)), Permacure 505 (Whyte Chemicals), Andamide 220 (Air Products), gamma-Aminopropyltriethyoxy silane (A1100 (OSi Specialties)), Dynasylan AMEO (Degussa-Huils Sivento) and A0750 (UCT), and hydrophobic fumed silica (CABOSIL TS-720 (Cabot)) and Aerosil R202 (Degussa). The phenolic accelerator component of the curing agent comprises about 0 to about 20 wt % of the curing agent, and is preferably about 5 to about 15 wt % of the curing agent.
The invention also provides a method for bonding articles together which comprises mixing the resin and curing agent components of the adhesive together, applying the adhesive composition of the invention in a liquid or paste form to a first article, bringing a second article in contact with the composition applied to the first article, and subjecting the applied composition to conditions which will allow the composition to cure to a composition having an irreversible solid form. The composition is typically distributed and stored in its two separate components. Thus, this invention includes adhesive compositions in both its two separate components, as it is typically stored and distributed, and its final, combined form, after it has been mixed and just prior to its application.
After application, in order to adhere articles together, the adhesive composition is subjected to conditions that will allow it to solidify and cure to a composition that has an irreversible solid form. Solidification (setting) occurs when the two components are mixed together at room temperature.
The invention can be better understood by the following non-limiting examples. All formulation components are listed by weight % unless otherwise noted.